Electric motor control system



Oct. 25, 1949. F. A. GROSS ETAL ELECTRIC MOTOR CONTROL SYSTEM Filed Oct. 14, 1947 m W Z M n VA war a m In 7 I a Patented a. 25, .1949

ELECTRIC MOTOR coNraoL srs'rm Fritz A. Gross, Weston, and Robert R. Dar-den, In,

Newton Highlands, Mara, assignors, by meone assignments, to Raytheon Air Beam, Inc., Newton, Mass, a corporation of Delaware Application October 14, 1947, Serial No. 779,746 12 Claims. (Cl. 318-282) This invention relates to a control system, and more particularly to a circuit for causing a controlled rotatable device tov be rotated back and forth in a repetitive manner through a predetermined angle or sector.

An object of this invention is to devise a control circuit, requiring no moving contacts, which controls a driving motor in such a manner as to automatically drive a driven object back and forth through a predetermined angle.

Another object is to devise a novel sense rectifier trigger-producing circuit for selectively triggering a pair of gas tubes.

A further object is to provide a motor control circuit using saturable reactors for control purposes. v

A still further object is to provide a simple yet reliable sector scan circuit for a rotatable directional search antenna.

The foregoing and other objects of the present invention will be best understood from the following description of an exemplification thereof, reference being had to the accompanying drawing, wherein the single figure is a schematic diagram of a system constructed in accordance with this invention.

In the system illustrated, a controlled or driven object I, such as a directional radiating antenna system for radiating ultra-high frequency waves, is to be caused to move repetitively back and forth through a predetermined but variable angle or sector, the position of the bisector of said angle being controllable by a remotely-located controllin member 2, such as a hand crank. In other words, both the relative direction and the angular width of the sector, through which object I is driven back and forth, or through which said object is caused to scan, are controllable. Of course, it is to be understood that controlling member 2 may take any other form which is known in systems of this type. The. controlled object i is driven back and forth by means of a two-phase alternating current motor 3, having a squirrel-cage rotor, for example, and having two separate field windings 4 and 5 displaced 90 in space from each other, as indicated. The field windings 4 and 5 are supplied from a suitable source of alternating current in a manner to be described hereinafter, in order to energize the field of the motor. Motor 3 drives a drive shaft 6, preferably through a gear reduction drive 1. Controlled object I is mounted upon and moved by the drive shaft 6, or said object may be driven from motor 3, directly or indirectly, through any other suitable means. The motion of the controlled object l-controls a synchro 8 consisting of a stator having a closed stator winding 9 and a rotatable armature l0 carrying a winding 1 l. The armature i0 is mounted upon and driven by the drive shaft 6, so that the position of armature in and winding l I at all times corresponds to the instantaneous position of controlled member I.

The armature winding Ii is supplied with alternating current from a pair of terminals l2 by means of a pair of leads It, said terminals l2 being energized from a reference source of alternating voltage, for example a standard l15-volt, (SO-cycle source. However, in some cases it may be desirable to provide a separate source of higher frequency for this purpose. Associated with the synchro 8 is a similar synchro l4 consisting of a stator having a closed stator winding l5 and a movable armature l6 carrying a winding I'l. Armature I6 is mechanically coupled to controlling object 2 in such a way that motion of said controlling object will rotate the armature It in a clockwise or counter-clockwise direction, depending upon the direction of motion of said controlling object. Three equally-spaced points on the stator winding 9 are connected by conductors l8, l9, and 20 to three similarly-spaced points on the stator winding l5.

As is well known, the alternating current field of the armature III is reproduced in the space within the stator winding l5, and induces a voltage in the armature winding l'l unless the arma-' ture i6 is substantially at right angles to said field. Thus, the amplitude of the voltage induced in the winding I1 is a measure of the deviation of armature In from the aforesaid right-angle relationship between armatures l0 and It, said induced voltage being proportional to the deviation of armature ill from the aforesaid rightangle relationship between the two armatures. The amplitude of the voltage induced in winding I1 is likewise a measure of the deviation of controlled member I from a certain position, which may be called the zero position, in which there is zero voltage induced in winding i I, this zero position corresponding to the bisector of the angle of the sector through which member I is to be scanned or moved back and forth.

The voltage generated in the armature winding i1 is applied as the input to a sense rectifier trigger-producing circuit which includes a pair of double triode vacuum tubes 2i and 22, and in order to so apply said voltage, one end of winding I1 is grounded and the other end is connected, through a condenser 23 and a resistor 24, to control grid 25 of tube It and to control grid 26 of tube 22, in parallel. In order to permit variation of the proportion of the voltage induced in winding I! which is applied to the said trigger-producing circuit, to thereby change the angular width of the sector through which object I is oscillated 3 plied to grids 28 and 26 may be supplied through any suitable variable means other than resistor 38. The upper end of resistor 30 is connected through a resistor 3| to a direct voltage supply line 32 which is energized from a suitable source of positive B voltage (not shown), on the order of 300 volts, for example.

In order to complete the input circuits to tubes 2| and 22, and in order to apply a direct potential, to cathodes 33 and 34 of tubes 2| and 22. which is above ground or is positive with respect to ground, one end of a lead 35 is connected to a. point between resistors 38 and 3| and the opposite end of said lead is connected to the midpoint of the secondary winding 36 of a cathode transformer 31. One end of said secondary winding is connected through a suitable resistor 38 to cathode 33 of tube 2|, while the opposite end f said winding is connected through a suitable resistor 39 to cathode 34 of tube 22. The primary winding 40 of step-down transformer 31 is connected directly to the terminals |2 of the alternating reference voltage source, so that the cathodes of tubes 2| and 22 are supplied with an alternating voltage of the same frequency as that of the voltage induced in armature winding H, the alternating voltages supplied to the two cathodes 33 and 34 being of opposite phase. A bypass condenser 4| may be connected between lead 35 and ground.

The two triode sections 2|a and 2 lb of the tube 2|, which have a common cathode 33 as shown, are connected as a two-stage cascade pulse amplifler or pulse transfer circuit, the anode 42 of the first triode 2 la being coupled through a condenser 43 to the input grid 44 of the second triode 2|b. The anode 45 of the second triode 2|b is connected through a condenser 46 to the control grid 41 of a gas tube 48, for example a thyratron,

in order to apply a positive trigger pulse, appearing on said anode, to said grid 41. A direct potential is supplied to anode 42 from line 32 through a resistor 48, while a direct potential is supplied to anode 45 from line 32 through a resistor 50. Similarly, the two triode sections 22a and 22b of tube 22, which have a common cathode 34 as shown, are connected as a two-stage cascade pulse amplifier or pulse transfer circuit, the anode of the first triode 22a being coupled through a condenser 52 to the input grid 53 of the second triode 22b. The anode 54 of the second triode 22b is connected through a condenser 55 to the control grid 56 of a second gas tube 51, which is similar to tube 48, in order to apply a positive trigger.

pulse, appearing on said anode, to said grid 56. A direct potential is supplied to anode 5| from line 32 through a resistor 58, while a direct potential is supplied to anode 54 from line 32 through a resistor 58.

Although tubes 2| and 22 are shown as being of the double triode type, it is desired to be brought out at this point that a pair of separate triode tubes may be used to replace each of the tubes 2| and 22, if desired, the proper connections for such an arrangement being obvious from the connections disclosed.

Gas tubes 48 and 51 are preferably tetrodes, tube 48 including, in addition to control grid 41, an anode 68, a shield grid 6|, and a cathode 62. Tube 51 includes, in addition to control grid 56, an anode 63, a shield grid 64, and a cathode 65. Shield grid 6| is connected to cathode 62 either externally or internally of tube 48, while shield grid 64 is connected to cathode 65 either externally or internally of tube 51. 'Cathodes 62 and 4 g: are both connected to ground, as indicated at In order to supply a negative bias to grid 41 of tube 48, said grid is connected through a resistor 61 to a point 66 on a suitable voltage divider, which point is located between a pair of serially-connected resistors 68 and 18, the free end of resistor 68 being grounded and the free end of resistor 10 being connected to a suitable source of negative C voltage (not shown), on the order of 105 volts, for example. Grid 56 of tube 51 is similarly negatively biased, by being ctamnected through a resistor 1| to the same point 6 Anode 68 is connected, through the direct current control winding 13 of a saturable core reactor 14 and through a resistor 15, to the positive supply line 32. Anode 63 is connected, through the direct current control winding 16 of a second saturable core reactor 11 and through a resistor 18, to supply line 32. Resistors 15 and 18 may be omitted if the windings 13 and 16 have ample resistance to sumciently limit the current through the gas tubes 48 and 51.

In order to stop the flow of anode current in either one of the two thyratrons when a positive impulse is applied to the grid of the other, a condenser 12 is connected between the two gas tube anodes 68 and 63. This condenser, with resistors 15 and 18, provides a so-called parallel direct current control circuit. When either tube 48 or tube 51 is conducting, condenser 12 charges with such polarity that the terminal thereof connected to the anode of the conducting tube is negative with respect to the other terminal thereof. Firing of the other tube by a positive grid impulse applies a negative voltage to the anode of the first tube, causing it to be extinguished.

The direct current control windings 13 and 16 of saturable reactors 14 and 11 are wound around the central legs of the corresponding three-legged reactors. The two outer legs of each reactor are of smaller cross-section than the central leg thereof, and are capable of becoming saturated by the flux created by the flow of current through the respective control winding. A pair of alternating current windings 19 and 88 are wound around the corresponding outer legs of reactor 14, and these two windings are connected in series in such a way, and the coils are wound in such a direction, that the two alternating fluxes established by the flow of alternating current through these two windings oppose each other in the central leg, so that no alternating voltage is induced in control winding 13. Similarly, a pair of alternating current windings 8| and 82 are wound around the corresponding outer legs of reactor 11, and these two windings are so wound and so connected in series that no alternating voltage is induced in the control winding 1 Field windings 4 and 5 of the two-phase motor 3 are connected together at a common point 83, and this point is connected by lead 84 to one side of a suitable source of alternating current power, which may be either the same as the reference alternating voltage source or may be a separate source. In the drawing, for purposes of simplicity, the motor' is indicated as being supplied with power from the reference voltage source. A condenser 85 is connected between the uncommon or free ends of windings 4 and 5 to give the required approximately phase difference between the voltages supplied to the two windings 4 and 5.

windingsllandfllareeonnectedinserieaas' while the free end of winding 8| is connected, by

means of a lead 88, to the uncommon or free end of field winding 4.

For a purpose to be described hereinafter, grid 44 of trlode section 2ib is connected, through a resistor 88, to anode 80 of gas tube 48, while grid 58 of triode section 22b is connected, through a resistor 8|, to anode of gas tube 81.

As described above, the gas tubes 48 and 51 are so interconnected that when one is fired, it automatically extinguishes the other. Since the tubes are supplied from a source of direct current, one or the other of tubes or 51 is always on, and the tubes are alternately fired. For example, if tube 48 is conducting, a positive impulse applied to the grid of tube 51 causes this latter tube to fire, extinguishing tube 48. Tube 51 remains on until a positive impulse is applied to the grid of tube 48, firing tube and thereby extinguishing tube 51. Tube 48 then remains on until a positive grid impulse is again applied to grid 58, again firing tube 51 and thereby extinguishing tube 48, and so on.

When tube 48 is conducting, current flows through the completed anode-cathode circuit therein and through the control winding 13 (of reactor 14) inseries therewith. This flow of cur-- rent through the control winding 13 causes saturation of the two outer legs of saturable reactor 14, decreasing the effective impedance of coils 19 and 80, linked with said legs, to substantially zero. This causes a substantial increase in the fiow of alternating current through said coils; The saturable reactors 14 and 11 are both designed in such a manner that they in efiect act as switches; that is to say, when gas tube 48 is not conducting, for example, there is no current flowing through control winding 13, and coils 19 and 88 have a substantially infinite impedance, so that there is substantially zero current flowing through them and the reactor 14 is then in effect an open switch. When tube 48 is fired, there is a substantial current flowing through control winding 13, coils 18 and 88 having a substantially zero impedance because of the saturation of the core, so that a large current then flows through said coils and reactor 14 is then in effect a closed switch. Saturable reactor 11 operates in a similar way. When tube 51 is nonconducting, the switch" 11 is opened and when tube 51 is conducting, the switch 11 is closed.

In designing the saturable reactors 14 and 11 to in efiect act as alternating current switches in the manner described, it should be kept in mind that the direct current flowing through the control winding of either reactor, as a result offiring the corresponding gas tube, should be of a value substantially greater than that necessary to cause saturation of the outer legs of the reactor, 50 that these legs remain saturated throughout the cycle of the alternating voltage applied to the alternating current coils on said outer legs.

Since gas tubes 48 and 51 are alternately fired in succession, "switches" 14 and 11 are alternately closed in succession, each switch" being opened when the other switch" is closed by the firing of the other gas tube.

When reactor 14 is saturated by the firing of gas tube 48, in effect a pair of circuits are closed through coils 18 and 88, one of them being traced as follows: left-hand terminal i2, lead 84, point 88, field winding 5, lead 88, coils 18, coil 88, point86, and lead 81 to the right-hand terminal 12. A parallel circuit extends from left-hand terminal i2 through lead 84, point 88, field winding 4, condenser 85, lead 88, coils 18 and 88, point 88, and lead 81, to right-hand terminal l2. It will be noted that, under these conditions, the current flows through fieldwinding 5 directly and through field winding 4 only in series with condenser 85. This results in an approximately phase shift of the voltage applied to winding 4 with respect to that applied to winding 5, and motor 8 rotates in a certain direction, clockwise for example.

When reactor 11 is saturated by the firing of gas tube 51, gas tube 48 is extinguished, the above circuits are in efiect broken, and a pair of circuits are closed through coils 8i and 82, one of them being traced as follows: left-hand terminal [2, lead 84, point 88, field winding 4, lead 89,

coil 8!, coil 82, point 86, and lead 81 to the righthand terminal l2. A parallel circuit extends from left-hand terminal l2 through lead 84, point 83, field winding 5, condenser 85, lead 89, coils 8| and 82, point 88, and lead 81, to right-hand terminal i2. Under these conditions, the current flows through field winding 4 directly and through field winding 5 only in series with condenser 85. This results in an approximately 90 phase shift of the voltage applied to winding 5 with respect to that applied to winding 4, and motor 3 then rotates in the opposite or counterclockwise direction,

Thus, by the operation of the circuit as above described using the pair of gas tubes 48 and 51 and the pair of saturable reactors 14 and 11 for the two-phase alternating current motor 8, controlled object I is driven in one direction while gas tube 48 is conducting, and is driven in the opposite direction while gas tube 51 is conducting. The sense rectifier trigger-producing circuit including tubes 2| and 22 functions, in a manner to be described, to provide a positive grid impulse to the gas tube not conducting, at the proper time (which is when the object 1 approaches the edge of the sector being scanned),

to switch conduction from one gas tube to the other to thereby reverse the direction of rotation of .motor 3. An impulse is provided, by said trigger circuit, to the proper gas tube, when said controlled object I is near each side edge of the sector being scanned, to, switch conduction from one gas tube to the other to thereby reverse the direction of rotation of motor 3 at each side edge of said sector.

It should be apparent that, due to mechanical inertia, even after an impulse is provided to switch conduction from one gas tube to the other, a certain time must elapse before the motor will slow down, come to a stop, and begin to rotate in the opposite direction. In other words the motor 3 does not and cannot reverse instantaneously. Therefore, there is a fixed minimum value of sector width, on the order of ten degrees for example, below which it is not possible to go without the system becoming unstable. This minimum value of sector width occurs when impulses for firing the gas tubes are produced simultaneously with the passage of object I through the bisector of the sector angle. In order to obviate the possibility of instability of the circuit, a limiting device must be provided on the sector width control to limit the adjustment of said control, in the direction of decreasing sector widths, to a point corresponding to the minimum stable sector width. For any particular drive motor used, the inertia or time lag is determinable.

The maximum sector width possible without the system becoming unstable is equal to 180 plus the minimum value of sector width. In order to obviate the possibility of instability of the circuit at this end of the sector width control, also, a limiting device must be provided on the sector width control, in the direction of increasing sector widths, to a point corresponding to the maximum stable sector width.

As previously explained, the peak amplitude of the alternating voltage induced in winding I! at any instant is a measure of the deviation of armature i and object I from the above-defined zero position at that instant. The maximum possible alternating peak voltage induced in winding l1, which we will term the maximum peak grid signal, is induced therein when armatures l0 and i6 are parallel to each other. For any particular synchros used, this voltage is known or predetermined.

A predetermined variable direct voltage bias, positive with respect to ground, is applied to grids 25 and 26 by the connection of grid lead 21 to the movable tap 29 on the potentiometer 30-3! connected between the positive voltage lead 32 and ground. Any suitable form of limiting device (not shown) is preferably provided to limit the minimum bias applied to grids 25 and 26 to a predetermined rather small positive voltage with respect to ground. This limiting device on the minimum bias provides the necessary limitation on the sector width control 29 in the direction of increasing sector widths. Any suitable form of limiting device (not shown) is also provided to limit the maximum bias applied to grids 25 and 26 with respect to ground. This limiting device on the maximum bias provides the necessary limitation on the sector width control 29 in the direction of decreasing sector widths.

An alternating voltage is applied to the oathodes 33 and 34 by secondary winding 36, the peak value of this voltage being made greater than the maximum peak grid signal defined above.

temating voltage applied to the cathodes is 80 volts, it the effective cutofl voltage of the tubes is 8 volts, and if the bias on the grids is 15 volts above ground when tap 29 is in its lowermost position, then the cathodes would have to be biased to a point Just slightly less than 133 volts above ground. Under these conditions, the voltage on grids 25 and 26 is swinging to 65 volts above ground (50 plus 15). In order to cause the triode sections 2m and 22a to Just conduct under these conditions, the cathode voltage must swing down to just less than 8 volts above the grid potential, or Just less than 73 volts (65 plus 8) above ground. The cathode voltage is swinging 60 volts downwardly (and also upwardly) about its fixed bias value, so that said fixed bias value must be Just less than 133 volts (73 plus 60).

It will be recalled that the cathode bias potential value determined as above described was for the greatest possible sector width, or the least possible value of bias voltage on grids 25 and 26, making it necessary for the maximum peak grid signal to be induced in winding I1 before one 01' the tubes 2 la or 22a goes above cutofi or reaches the conducting condition. The maximum peak grid signal is induced in winding ll when armatures l0 and [6 are parallel to each other, so that under these conditions, as will later appear, a sector width of substantially 180 is obtained, plus of course the minimum possible sector width, which is the angle through which object I travels during the time interval required due to mechanical inertia of motor 3.

Grid 44 of triode section 2ib is tied to anode 60 of gas tube 48 through a resistor 90, as above described. The potential of anode 60 is therefore applied to said grid through said resistor,

- as a bias voltage for said grid. When tube 48 Tubes 2i and 22 preferably have such characteristics that cutoff thereof is efiected when a predetermined rather small negative voltage with respect to the cathodes thereof is applied to the corresponding control grids 25 and 26.

The direct voltage applied to cathodes 33 and 34 by lead 35 biases these cathodes to a voltage, which is positive with respect to ground 92, or is above ground, by a substantial amount. This amount must be just slightly less than the sum of the maximum peak grid signal, the peak value of the alternating voltage applied to the cathodes 33 and 34, the effective grid-cathode cutofi voltage of the tubes, and the minimum possible grid bias voltage (that applied when tap 29 is in its lowest position on resistor 30) This potential of the cathodes with respect to ground must be just less than the aforesaid sum, in order to insure that the tubes 2ia and/or 22a will conduct under these conditions of the extreme maximum sector width. For example, if the maximum peak grid signal is 50 volts, if the peak value of the alis non-conducting, the potential on anode 60 thereof is the high positive potential of line 32, so that a positive potential is placed on grid 44 with respect to cathode 33, causing grid current to be drawn, so that the net potential on grid 44 is that of line 32 less the voltage drops in resistors 15 and 90, and winding 13. This net potential on grid 44 is small as compared to that of line 32, but is positive as compared to that of the cathode 33. This net potential is less than the cutoff value of triode section 2|b, so that, under these conditions, triode section 2lb is in the conducting condition or is passing plate current. When tube 46 is triggered or fired by a positive impulse applied to its grid 41, the voltage on anode 60 drops a substantial amount, to a value substantially equal to the low voltage drop of the arc discharge in said tube. This low voltage is now applied to grid 44 and is sufilciently negative with respect to cathode 33 (which, it will be remembered, is biased a substantial amount positive with respect to ground) to cut oil the plate current in triode section Zlb. Therefore, when and as long as tube 48 is nonconducting, triode section 2lb is conducting, but when and as long as tube 48 is conducting, triode section 2|b is non-conducting or is cut oil.

Grid 53 of triode section 22b is tied to anode 63 of gas tube 51 through a resistor 9|, as above described. This connection functions similarly to that just described, to cause triode section 22b to conduct when and as long as tube 51 is nonconducting, and to cause triode section 22b to be out off when and as long as tube 51 is conducting.

We will assume as a starting point that gas tube 48 is conducting, and will assume that when this tube is conducting, motor 3 is caused to rotate in such a direction as to rotate armature iii in a clockwise direction. Under these conditions, when gas; tube 48 is conducting. as tube 61 is extinguished, triode section 2Ib is cut on, and trlode section 22b is conducting, due to the connections above described.

When the controlled object or antenna. I is driven by motor 3 so as to produce an angular displacement of the armature I with respect to armature I 6 from the zero or perpendicular relation illustrated, a voltage appears across the armature winding II, as already described. Assuming first a steady-state condition, which means that the armature I6 is stationary, the voltage appearing across winding I'I will be either in phase or 180 out of phase with the reference voltage at the input terminals I2, depending upon whether armature III is on one side or the other of its zero position with respect to armature I6. If we assume that the voltage in winding I1 is in phase with the reference voltage when armature I0 moves clockwise from its zero position with respect to armature I6, then the voltage in winding I! will be 180 out of phase with the reference voltage when armature I0 moves counterclockwise from its zero position with respect to armature I6.

As described above, triode sections 2Ia and 22a are normally non-conducting, due to the substantial bias of cathodes 33 and 34 above ground. The voltage in'winding I1 is applied to the two grids 25 and 26 in parallel, as previously described. -Windings 36 and 46 of cathode transformer 31 are so related that when a voltage in phase with the reference voltage is applied to grids 25 and 26, the voltages applied to grid 26 and cathode 34 are 180 out of phase with each other, so that one of these two voltages is increasing with respect to its own zero line while the other is decreasing with respect to its own zero line.

As explained above, the zero or base line (with respect to ground), about which the reference alternating voltage applied to cathodes 33 and 34 oscillates, is determined by the direct voltage applied to said cathodes by lead 35, and in the example given is just slightly less than 133 volts above ground. Since cathodes 33 and 34 are connected to opposite ends of winding 36, the alternating voltages applied to the two cathodes are 180 out of phase with respect to each other. The zero or base line(with respect to ground), about which the alternating voltage applied to grids 25 and 26 from winding I'I oscillates, is determined by the setting of tap 29 on resistor 30, this setting being capable of manual adjustment.

As explained heretofore, the voltage induced in winding I1 is proportional to the angular deviation of armature I0 from the right-angle relationship between the two armatures I0 and I6, so

' that as this angular deviation increases because of the angular movement of armature In, the amplitude of the alternating voltage applied to grids 25 and 26 increases.

Under the conditions assumed, with gas tube 48 conducting and armature Ill rotating in a clockwise direction from the zero position illustrated, the alternating voltage applied to grids 25 and 26 swings upward from its zero or base line during alternate half-cycles, and the amplitude of this voltage increases as the clockwise deviation of armature I0 increases from the zero position illustrated. During the upward swings of the alternating voltage applied to grid 26, the reference alternating voltage applied to cathode 34 is swinging downwardly from its zero line, so that the grid voltage peaks occur at the same time as do the points at which the cathode 34 reaches its lowest or minimum voltage above ground. As the voltage on grid 26 continues to increase, said voltage finally attains a peak value (65 volts above ground in the example given) which is sufficient, because the grid voltage peak occurs simultaneously with the minimum value of cathode voltage, to cause triode section 22a to conduct. The sudden conduction of tube 22:: increases the plate current thereof and produces a negative voltage impulse at anode 5|, this impulsebeing transmitted through condenser 52 and being utilized to cut off triode section 22b which, as stated above, was previously conducting. The cutting oil of tube 221) produces a rectified positive impulse or trigger at anode 54, which impulse is transmitted through condenser 55 to grid '56, firing tube 61 and thereby extinguishing tube 48. Since tube 51 is now conducting, motor 3 reverses its direction of rotation and now drives antenna I in a direction corresponding to a counterclockwise direction of rotation of armature I0.

Although the alternating voltage in winding I1 is applied to both grids 25 and 26 in parallel, triode section 2Ia cannot conduct, rather than triode section 22a, in an improper manner. This is because of the fact that, during the half-cycles in which the voltage on cathode 33 reaches its minimum value, when conduction could occur, the voltage on' grid 25 is swinging downwardly from its zero line and has a value, throughout these half-cycles, substantially beyond the gridcathode cutoff voltage of the tube. As an added protection, triode section 2") is kept out off while tube 48 is conducting. A positive impulse, to fire one of the gas tubes, can be produced only by the cutting oil? of either of the triode sections 2Ib or 22b. No such positive impulse can be procut off during this time.

The absolute value of peak grid voltage at any time is the result of two components, one being the amount of angular deviation of armature l3 from its zero position and the other being the absolute value of the direct grid bias, which latter value is variable by movement of tap 29 on resistor 30. By moving tap 29 upwardly from its lowermost position, the direct voltage bias on grids 25 and 26 is increased, moving the zero or base line of the alternating grid voltage upwardly. When this zero line is moved upwardly, the predetermined peak value of alternating grid voltage necessary to cause sections 2 la or 22a to conduct,

to cause reversal of motor 3, is reached at a' smaller angular deviation of armature Ill. Thus the angle through which antenna I rotates or scans is decreased, and the sector width is reduced. In an analogous manner, by moving tap 29 downwardly, the sector width may be increased. Thus, tap 29 provides a control for the width of the sector desired to be scanned by antenna I.

To return to a description of operation of the system, when tube 51 fires, triode section 2Ib is again allowed to conduct, due to the extinguishment of tube 48, and triode section 22b is held cut off by the conduction of tube 51.

While armature I0 is rotating in the counterclockwise direction, returning toward the zero position, the phase relationships between the cathode and grid voltages of tubes 2: and 22a are the same as heretofore explained, so that triode section 2Ia cannot conduct. The holding of section 222) in the cutoff condition, by conduc- 2,486, 1 iii 11 tion of tube 31, assists in preventing spurious positive impulses from being applied to grid 58 of tube 51 after said tube has been fired.

When armature I passes beyond the zero position, rotating in the counterclockwise direction, the voltage induced in winding I! will be 180 out of phase with the reference voltage, so that now the voltage applied to grids and 26 will be in phase with the voltage applied to cathode 34 and 180 out of phase with the voltage applied to cathode 33. The amplitude of the alternating grid voltage increases as the counterclockwise deviation of armature l0 increases from the zero position. Due to the phase relations now existing, the grid voltage peaks now occur at the same time as do the points at which cathode 33 reaches its lowest or minimum value above ground. As the voltage on grid 25 continues to increase, said voltage finally attains a peak value which is sufficient, because said peak occurs simultaneously with the minimum value of cathode voltage, to cause triode section 2la to conduct. This peak value is reached when armature ID has a deviation on one side of its zero position equal to the deviation on the opposite side when the previous reversal of motor 3 occurred. In other words, the zero position of armature l0 bisects the sector through which armature l0 moves or scans.

The conduction of tube 2la produces a negative voltage impulse at anode 42, this impulse being transmitted through condenser 43 and being utilized to cut off triode section 2ib, which was previously conducting. The cutting off of tube 2|b produces a rectified positive impulse or trigger at anode 45, which impulse is transmitted through condenser 46 to grid 41, firing tube 48 and thereby extinguishing tube 51. Since tube 48 is now conducting, motor 3 again reverses its direction of rotation, and drives antenna l in the original direction, that is, in a direction corresponding to a clockwise rotation of armature l0.

Triode section 22a cannot conduct, rather than triode section 2la, at this edge of the sector, in an improper manner. During the half-cycles in which the voltage on cathode 34 reaches its minimum value, when conduction could occur, the voltage on grid 28 is swinging downwardly from its base or zero line and has a value, throughout these half-cycles, substantially beyond the gridcathode cutoff voltage of the tube. As an added protection, triode section 22b is kept out off while tube 51 is conducting. No positive impulses can be produced by the cutting oif of section 22b, even if section 22a does conduct improperly while tube 51 is conducting, since section 221) is already cut off during this time.

When tube 48 again fires, triode section 22b .is again allowed to conduct, due to the extinguishment of tube 51, and triode section 2lb is held out off, by the conduction of tube 48.

A saving in system current consumption is eifectuated by the maintaining of triode sections 2!!) and 22b out off while the corresponding gas tubes are conducting, after these sections have produced a positive impulse as desired. I

While armature III is again rotating in the clockwise direction, returning toward the zero position, the phase relations between the cathode 12 tube 48, assists in preventing spurious positive impulses from being applied to grid 41 of tube 48 after said tube has been fired, which impulses could be produced at the extreme edge of the sector during the mechanical time lag of motor 3 and armature l0, since the mid voltage at this edge is sufilcient to cause conduction in tube 2 in.

When armature III has returned to the zero position, rotating in the clockwise direction as a result of the firing of tube 48, the assumed starting point of the above-described operation has again been reached, and the process repeats itself as long as the system is energized. The system therefore operates or functions to produce oscillatory angular motion of antenna I back and forth through a sector, the angular width of which is variable by movement of tap 29.

Reversal of the direction of rotation of motor 3 can occur only when armature l0 has a predetermined angular deviation on either side of its zero position with respect to armature I6, slnce it is only when this predetermined angular deviation exists that there is suflicient voltage induced in winding I1, and applied to grids 25 and 26, to cause current fiow in tubes 2Ia or 22a. Therefore, armature H reciprocates or oscillates back and forth through a sector, the bisector of the angle of which is determined by the position of armature l6, and by rotation of crank 2 to rotate armature [6, the direction of the bisector of the angle through which antenna l moves may be varied at will.

The double triode tubes 2| and 22 produce a rectified positive voltage impulse or trigger at either anode 45 or anode 54, depending on the relative direction or sense of armature H) with respect to its zero position. The circuit including tubes 2| and 22 may therefore be termed a sense rectifier trigger circuit.

It will be seen, from all of the above, that we have devised an efficient control circuit, requiring no moving contacts, for controlling a driving motor in such a manner as to automatically drive a driven object back and forth through a predetermined angle or sector.

Of course, it is to be understood that this invention is not limited to the particular details as described above, as many equivalents will suggest themselves to those skilled in the art. For example, instead of the three-phase synchros 8 and I4 illustrated, two-phase synchros, known as resolvers, could alternatively be used for the same purpose, if desired for greater accuracy. Although, in the circuit shown, the signal voltage is applied to the two grids 25 and 26 in the same sense and the reference voltage is applied to the two cathodes 33 and 34 in opposite senses, the signal voltage could equally well be applied to the cathodes and the reference voltage to the grids, while one 'of the voltages could be applied to the two grids in opposite senses and the other voltage to the two cathodes in the same sense; in fact, any combination of reference and signal voltages, and the same or opposite senses, could be used, so long as either the reference or the signal voltage is applied to the cathodes and the other to the grids, and so long as the grids are fed in the same sense and the cathodes in opposite senses, or vice versa. Various other variations will suggest themselves. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of this invention within the art.

What is claimed is:

1. In a motor control system, an alternating assaru adapted to act as a closed alternating current.

switch in response to the flow of direct current through said saturating winding, means connecting the alternating current winding of said reactor between a source of alternating current and said motor, and discharge means in series with said saturating winding and a source of direct current for causing direct current to flow through said saturating winding to close said switch and thereby energize said motor from said source.

2. In a motor control system, an alternating current motor, a saturable reactor having at least a direct current saturating winding and an alternating current winding, said reactor being adapted to act as a closed alternating current switch in response to the flow of direct current through said saturating winding, means connecting the alternating current winding of said reactor between a source of alternating current and said motor, and means for causing direct current to flow through said saturating winding to close said switch and thereby energize said motor from said source, said last-named means comprising a controllable gas discharge tube connected in sebeing adapted to act as closed alternating current switches in response to the flow of direct current through the saturating windings thereof, means connecting the alternating current winding of one of said reactors between a source of alternating current and one motor winding, means connecting the alternating current winding of the other reactor between said source and the other motor winding, and means for causing direct current to flow alternately through the saturating windings of said two reactors to close the corresponding switches to thereby energize said motor from said source successively in opposite senses, said last-named means including a ries between a source of direct current and said saturating winding.

3. In a motor control system, a two-phase motor having a pair of windings, a pair of saturablereactors each having at least a direct current saturating winding and an alternating current winding, said reactors being adapted to act as closed alternating current switches in response to the flow of direct current through the saturating windings thereof, means connecting the alternating current winding of one of said reactors between a source of alternating current and one motor winding, means connecting the alternating current winding of the other reactor between said source and the other motor winding, and controllable discharge means connected in series with each of said saturating windings and a source of direct current for causing direct current to fiow alternatively through the saturating windings of said two reactors to close the corresponding switches to thereby energize said motor from said source in opposite senses.

4. In a motor control system, a two-phase motor having a pair of windings, a pair of saturable reactors each having at least a direct current saturating winding and an alternating current winding, said reactors being adapted to act as closed alternating current switches in response to the flow of direct current through the saturating windings thereof, means connecting the alternating current winding of one of said reactors between a source of alternating current and one motor winding, means connecting the alternating current winding of the other reactor between said source and the other motor winding, and means for causing direct current to flow alternatively through the saturating windings of said two reactors to close the corresponding switches to thereby energize said motor from said source in opposite senses, said last-named means comprising a pair of controllable gas discharge tubes, one of said tubes being connected in series between a source of direct current and each of said saturating windings.

5. In a motor control system, a two-phase motor having a pair of saturable reactors each having at least a direct current saturating winding and an alternating current winding, said reactors pair of alternately-conducting gas discharge tubes, one of said tubes being connected in series between a source of direct current and each of said saturating windings.

6. In a motor control system, a tw0-phase motor having a pair of windings, a pair of saturable reactors each having at least a direct current saturating winding and an alternating current winding, said reactors being adapted to act as closed alternating current switches in response to the flow of direct current through the saturating windings thereof, means connecting the alternating current winding of one of said reactors between a source of alternating current and one motor winding, means connecting the alternating current winding of the other reactor between said source and the other motor winding, a pair of controllable gas discharge tubes, one of said tubes being connected in series between a source of direct current and each of said saturating windings, and means for causing said tubes to alternately conduct to thereby cause direct current to flow alternately through the saturating windings of said two reactors.

7. In a motor control system, a two-phase motor having a pair of windings, a pair of saturable reactors each having at least a direct current saturating winding and an alternating current winding, said reactors being adapted to act as closed alternating current switches in response to the flow of direct current through the saturating windings thereof, means connecting the alternating current winding of one of said reactors between a source of alternating current and one motor winding, means connecting the alternating current winding of the other reactor between said source and the other motor winding, a pair of controllable gas discharge tubes, one of said tubes being connected in series between a source of direct current and each of said saturating windings, a source of alternating volt age reversible in phase, and means responsive to the phase of said alternating voltage. for causing a corresponding one of said tubes to conduct to thereby causedirect current to flow through the corresponding reactor saturating winding.

8. In a motor control system, a two-phase motor having a pair of windings, a pair of saturable reactors each having at least a direct current saturating winding and an alternating current winding, said reactors being adapted to act as closed alternating current switches in response to the flow of direct current through the saturating windings thereof, means connecting the alternating current winding of one of said reactors between a source of alternating current and one motor winding, means connecting the alternating current winding of the other reactor between said source and the other motor winding, a pair of controllable gas discharge tubes,

one of said tubes being connected in series between a source of direct current and each of said saturating windings, a source of signal voltage reversible in phase and of a predetermined frequency, and a sense rectifier including a pair of electron discharge tubes having their grids connected to said signal voltage source and their cathodes connected to a reference voltage source of said predetermined frequency, said sense rectifler being responsive to the phase sense of said signal voltage for causing a corresponding one of said gas tubes to conduct to thereby cause direct current to flow through the corresponding reactor saturating winding.

9. In a sector scan system, a driven member adapted to be driven back and forth through a sector, a two-phase motor for driving said member through saidsector, means forcontrolling the extent of said sector comprising means for generating an alternating voltage in response to adeviation of said driven member from a predetermined position, said voltage being reversible in phase sense depending upon the direction of said deviation, a pair of saturable reactors each having at least a direct current saturating winding and an alternating current winding, said reactors being adapted to act as closed alternating current switches in response to the flow of direct current through the saturating windings thereof, means connecting the alternating current winding of one of said reactors between a source of alternating current and one motor winding, means connecting the alternating current winding of the other reactor between said source and the other motor winding and means responsive to the phase sense of said alternating voltage for causing direct current to flow alternatively through one or the other of said saturating windings depending upon said phase sense, said last named means being responsive to said alternating voltage only when said voltage exceeds a predetermined value.

10. In a sector scan system, a driven member adapted to be driven back and forth through a sector, a two-phase motor for driving said mem- 5 ber through said sector, means for generating an alternating voltage in response to a deviation of said driven member from a predetermined position, said voltage being reversible in phase sense depending upon the direction of said deviation, a 50 pair of saturable reactors each having at least a direct current saturating winding and an alternating current winding, said reactors being adapted to act as closed alternating current switches in response to the flow of direct current through 55 the saturating windings thereof, means connecting the alternating current winding of one of said reactors between a source of alternating current and one motor winding, means connectin th alternating current winding of the other reactor 60 between said source and the other motor winding, a pair of controllable gas discharge tubes, one of said tubes being connected in series between a source of direct current and each of said saturating windings, and means responsiv to the 65 phase sense of said alternating voltage for causing a corresponding one of said tubes to conduct to thereby cause direct current to flow through the corresponding reactor saturating winding.

11. In a. sector scan system, a driven member 70 response to a deviation of said driven member 75 16 from a predetermined position, said voltage being reversible in phase sense depending upon the direction of said deviation, 9. pair of saturable reactors each having at least a direct current saturating winding and an alternating current winding, said reactors being adapted to act as closed alternating current switches in response to the flow of direct current through the saturating windings thereof, means connecting the alternating current winding of one of said reactors between a. source of alternating current and one motor winding, means connecting the alternating current winding of the other reactor between said source and the other motor winding, and a sense rectifier including a pair of electron discharge tubes having their grids connected to said signal voltage and their cathodes connected to are!- erence voltage source of said predetermined frequency, said sense rectifier being responsive to the phase sense of said signal voltage for causing direct current to flow alternatively through onethe extent of said sector comprising means for adjustin the minimum value of said signal voltage to which said sense rectifier will respond.

12. In a sector scan system, a driven member adapted to be driven back and forth through a. sector, a two-phase motor for driving said member through said sector, means for generating a signal voltage of a predetermined frequency in response to a deviation of said driven member from a predetermined position, said voltage being reversible in phase sense depending upon the direction of said deviation, a pair of saturable reactors each having at least a direct current saturating winding and an alternating current winding, said reactors being adapted to act as closed alternating current switches in response to the flow of direct current through the saturating windings thereof, means connecting the alternating current winding of one of said reactors between a source of alternating current and one motor winding, means connecting the alternating current winding of the other reactor between said source and the other motor winding, a pair of controllable gas discharge tubes, one of said tubes being connected in series between a source of direct current and each of said saturating windings, and a sense rectifier including a pair of electron discharge tubes having their grids connected to said signal voltage and their cathodes connected to a reference voltage source of said predetermined frequency, said sense rectifier being responsive to the phase sense of said signal voltage for causing a corresponding one of said gas tubes to conduct to thereby cause direct current to flow through the corresponding reactor saturating winding.

FRITZ A. GROSS. ROBERT R. DARDEN, JR.

REFERENCES CITED The following references are of record in the file-of this patent:

UNITED STATES PATENTS Number Name Date 1,955,322 Brown Apr. 17, 1934 1,965,416 Howard July 3, 1934 2,070,462 White Feb. 9, 1937 2,402,210 Ryder et al June 18, 1946 2,414,936 Edwards et a1 Jan. 28, 1947 2,424,568 Isbister et al. July 29, 1947 

